1. Technical Field
The present invention generally relates to a method for recording, storing, and reproducing information. More specifically, the invention relates to such a method using an apparatus for detecting information in accordance with an interaction between a probe and a sample. Still more specifically, the present invention relates to a medium to be used for recording, storing and reproducing information.
2. Description of the Related Art
There is currently much interest in the potential applications of scanning probe microscopy (SPM) technology. SPM has been used for fundamental studies of local frictional properties such as the boundary lubrication of molecular thin films between a recording head and the respective thin film recording media in magnetic recording. SPM storage techniques use scanning probe methods for recording, storing and reproducing information. Examples include Scanning tunneling microscopy (STM) and Atomic Force Microscopy (AFM). Utilizing such techniques, modifications of a storage medium, such as changing surface topography or modifying physical characteristics, can be induced and detected by measurement of physical quantities, e.g. measuring the force between a probe tip and the medium.
As IT equipment becomes smaller due to continuing improvements in microelectronic development, conventional data storage utilizing rigid disk drives becomes a limiting factor in efforts to reduce the size of such equipment. Conventional storage devices are limited by the incorporation of moving parts which reduces reliability and ruggedness.
Semiconductor memories, on the other hand, are limited in terms of both size and cost. There is a growing requirement for high-capacity storage devices having a significantly reduced size, especially in multimedia applications which rely on very high data rate and low access times.
Data storage using scanning probe techniques have the potential for high storage density (cf. H. J. Mamin et al., xe2x80x9cTip-based data storage using micromechanical cantileversxe2x80x9d, Sens. actuators A, vol. 48, pp. 215-219, 1994) and approaches to parallelize storage devices are promising high data rates (cf. U.S. Pat. No. 5,835,477 to G. Binnig et al.). Highly parallelized devices are particularly reliant on a high degree of integration and lowest possible crosstalk between individual channels.
Scanning probe techniques (SPT) are well known techniques for detecting physical quantities on a nanometer scale. Physical quantities are detected by observing the interaction between a sharp tip probe and a sample. Examples of quantities detected in this manner include tunneling current, atomic force, magnetic force, electrostatic force, light density. These techniques resolve a spatial resolution from about 1 nm to about 100 nm. Due to this enormous spatial resolution, several approaches for using such techniques for digital data storage have been made.
Bits ranging in size from 1 nm to 100 nm were already written by such techniques as tunneling current, surface deformation of the medium by heating the tip (cf. G. Binnig et al., xe2x80x9cThermomechanical writing with an atomic force microscope tipxe2x80x9d, Appl. Phys. Lett., vol 61, pp. 1003-1005, 1992, and H. J. Mamin: xe2x80x9cThermal writing using a heated atomic force microscope tipxe2x80x9d, Appl. Phys. Lett., vol 69 pp. 433-435, 1996), and E-field induced charge deposition (cf. I. Fujiwara et al., xe2x80x9cHigh density charge storage memory with scanning probe microscopyxe2x80x9d, Jap. J. Appl. Phys. vol. 35, pp. 2764-2789, 1996; and B. Terris et al., xe2x80x9cLocalized charge force microscopyxe2x80x9d, J. Vac. Sci. technol A, Vol. 8 No.1, pp. 374-377, January/February 1990). The information stored was read back by appropriate SPT.
Utilization of field-induced reversible switching processes in some specific organometallic materials is described by Yamaguchi (S. Yamaguchi et al., xe2x80x9cSurface Modifications on Charge-Transfer Complexes using Scanning Probe Microscopyxe2x80x9d, Mat. Res. Soc. Symp. Proc vol 3, 1993). Yamaguchi describes a switching phenomenon in which the resistivity of a material switches from high resistivity to low resistivity if the electric field beneath a probe exceeds a material specific threshold. Resistivity can be switched back by applying a field of negative polarity. A similar effect is identified for optically induced switching. A kind of readback was performed by optical inspection of the material surface.
U.S. Pat. No. 5,535,185 describes an apparatus implementing SPT for recording/reproduction of information using physical quantities like tunneling current, electric field radiation current, contact current, electrostatic capacitance, atomic force, magnetic force, and electrostatic force with adaptive recording/erasing conditions. A single probe system with additional control circuits is demonstrated.
Another approach is proposed in U.S. Pat. No. 5,835,477 which uses a highly parallel array of probes on a storage medium. Recording/reproduction follows the above-described principles.
All of the above mentioned SPT approaches are characterized by the use of a write stimulus on a probe, causing a modification of the storage medium. Examples of such modifications are electric, magnetic, optical and elastic characteristics as well as surface topography or thickness. Stored information is read back by measurement of the modified physical quantity, detected by the probe (e.g. resonance frequency of cantilever, bending stress of cantilever, resistance change due to cooling effects).
All of these methods incorporate the following scheme. First, information is written to a medium via a transducer. The information is then stored by physical modifications of the storage medium. Thus, the storage medium itself is passive, being an object of modification. Recording and reproduction is solely performed by detecting changes in the probe response. Information read back is performed by again detecting modifications of the storage medium via a transducer (writing device/reading device). In the interest of medium reusability, means to erase the medium are usually provided.
Since all recording and reproduction is done via a probe, the probe must be highly complex. It must carry write and read stimuli as well as a readback signal. To operate such a probe, a very complex electric system is required to be located on a limited space. In particular, array-like structures, as proposed by G. Binnig et al. (U.S. Pat. No. 5,835,477), rely on a highly dense design while maintaining minimum interference between probe elements. Such dense configurations regularly suffer from crosstalk, noise, mechanical instability and fabrication problems.
Furthermore, use of probe transducers for recording and reproduction excludes several physical characteristics (e.g. like optical transmission effects) from use in storage applications. Due to its limited impact on functionality, optimization of the passive medium results in small performance improvements.
It is therefore an object of the invention to provide a method and apparatus which improves scanning probe storage systems.
It is another object of the invention to provide a method and apparatus capable to add an active functionality to the storage medium.
The present invention features an active storage medium. This storage medium plays an active part in recording, erasure and reproduction either in part or in a combination of these processes. This active feature is characterized by a signal path crossing the medium during the corresponding process(es). The active role may be one or all, but is not limited to one of the following:
writing via medium;
readback via medium;
erasure via medium; and
heating via medium.
Several physical characteristics may be used for this. Examples for such quantities are electrical conductivity, optical characteristics, e.g. transparency/reflectivity, or electrical capacity. This list is given for example only and not limiting. The medium may be patterned, especially advantageous on a storage-field scale.